1. Field of the Invention
The present invention relates to an apparatus for loading fibers in a fiber suspension with a chemical compound, and, more particularly, to an apparatus for loading fibers in a fiber suspension with calcium carbonate.
2. Description of the Related Art
A paper-making machine receives a fiber suspension including a plurality of fibers, such as wood fibers, which are suspended within an aqueous solution. The water is drained and the fiber suspension, of more than 2,200 cu. ft. up to 132,000 cu. ft. per day for today's paper making process, which is dried in the paper-making machine to increase the fiber content and thereby produce a fiber web as an end product.
The fiber web produced by the paper-making machine typically includes organic wood fibers and inorganic fillers. A known inorganic filler is calcium carbonate, which may be added directly to the fiber suspension (direct loaded calcium carbonate). It is also known to chemically load the fibers within a fiber suspension with calcium carbonate in the lumen and walls of the individual fibers (fiber loaded calcium carbonate). The fiber loaded calcium carbonate increases the strength of the paper compared with a direct loaded calcium carbonate (adding calcium carbonate directly to the fiber suspension) at the same loading (filler) level. This yields an economic advantage in that the filler level of the paper is increased by replacing the more expensive fiber source (wood fibers) with calcium carbonate. The finished paper web has higher strength properties due to the increased filler levels of the calcium carbonate. In contrast, the strength properties of a finished web using direct loaded calcium carbonate is less.
For example, U.S. Pat. No. 5,223,090 (Klungness, et al.) discloses a method for chemically loading a fiber suspension with calcium carbonate. In one described method, calcium oxide or calcium hydroxide is placed within a refiner unit and carbon dioxide is injected into the refiner unit at a specified pressure. The fiber suspension is maintained within the refiner for a predetermined period of time to ensure that a proper chemical reaction and thus proper chemical loading of the fiber suspension occurs. In another described method, a fiber suspension with calcium oxide or calcium hydroxide is introduced into a 20 quart food mixer and carbon dioxide gas is injected into the mixer at a specified pressure. Using either the refiner or the food mixer, both methods utilize a batch processing method for processing only a small amount of the fiber suspension at a time. Because of the large amount of fiber suspension which is required at the wet end of a paper-making machine, a batch process requires that the chemically loaded fiber suspension be transferred to another holding tank for ultimate use in a paper-making machine.
What is needed in the art is an apparatus for chemically loading a fiber suspension for use in a paper-making machine with an adequate output of a chemically loaded fiber suspension which allows commercialization of such a chemical loading process.